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Eutrophication The magnitude of the risk of
ecosystem eutrophication and its geographical coverage has diminished
only slightly over the years. The predictions for 2010 and 2020 indicate
that the risk is still widespread over Europe. This is in conflict with
the EU's long-term objective of not exceeding critical loads of
airborne acidifying and eutrophying substances in sensitive ecosystem
areas (National Emission Ceilings Directive, 6th Environmental Action
Programme, Thematic Strategy on Air Pollution).
Acidification The situation has considerably
improved and it is predicted to improve further. The interim
environmental objective for 2010 (National Emission Ceilings Directive)
will most likely not be met completely. However, the European ecosystem
areas where the critical load will be exceeded is predicted to have
declined by more than 80 % in 2010 with 1990 as a base year. By 2020, it
is expected that the risk of ecosystem acidification will only be an
issue at some hot spots, in particular at the border area between the
Netherlands and Germany.
Ozone (O 3 ) Most
vegetation and agricultural crops are exposed to ozone levels exceeding the
long-term objective given in the EU Air Quality Directive. A significant
fraction is also exposed to levels above the 2010 target value defined in the
Directive. Concentrations in 2008 were on the average higher than in 2007. The
effect-related accumulated concentrations, addressing exposure of crops to
ozone over several summer months, shows large year-to-year variations, there is
a non-significance tendency to increase.

Key messages

EutrophicationThe magnitude of the risk of
ecosystem eutrophication and its geographical coverage has diminished
only slightly over the years. The predictions for 2010 and 2020 indicate
that the risk is still widespread over Europe. This is in conflict with
the EU's long-term objective of not exceeding critical loads of
airborne acidifying and eutrophying substances in sensitive ecosystem
areas (National Emission Ceilings Directive, 6th Environmental Action
Programme, Thematic Strategy on Air Pollution).

AcidificationThe situation has considerably
improved and it is predicted to improve further. The interim
environmental objective for 2010 (National Emission Ceilings Directive)
will most likely not be met completely. However, the European ecosystem
areas where the critical load will be exceeded is predicted to have
declined by more than 80 % in 2010 with 1990 as a base year. By 2020, it
is expected that the risk of ecosystem acidification will only be an
issue at some hot spots, in particular at the border area between the
Netherlands and Germany.

Ozone (O3)Most
vegetation and agricultural crops are exposed to ozone levels exceeding the
long-term objective given in the EU Air Quality Directive. A significant
fraction is also exposed to levels above the 2010 target value defined in the
Directive. Concentrations in 2008 were on the average higher than in 2007. The
effect-related accumulated concentrations, addressing exposure of crops to
ozone over several summer months, shows large year-to-year variations, there is
a non-significance tendency to increase.

What progress is being made towards the targets for reducing the exposure of ecosystems to acidification, eutrophication and ozone?

Exceedance of critical loads for eutrophication due to the deposition of nutrient nitrogen in 2000

Note:The results were computed using the 2008 Critical Loads database hosted by the Coordination Centre for Effects (CCE).

Exposure of agricultural area to ozone (exposure expressed as AOT40 in (μg/m³).h) in EEA member countries

Note:In the Air Quality Directive (2008/50/EC) the target value for protection of vegetation is set to 18 000 (μg/m³).h while the long-term objective is set to 6 000 (μg/m³).h. Due to lack of detailed land cover data and/or rural ozone data Iceland and Norway are not included until 2006 and onwards. Switzerland have not been included in the analysis for the entire period 1996-2007 due to the same reasons. Turkey is not included in the analysis 1996-2008.

Exposure of forest area to ozone (exposure expressed as AOT40 in (μg/m³).h) in EEA member countries

Note:UNECE has set a critical level for protection of forest to 10 000 (μg/m3).h. Since 2004 a growing number of EEA member countries have been included. In 2004 Bulgaria, Greece, Iceland, Norway, Romania, Switzerland, and Turkey have not been included. In 2005-2006 Iceland, Norway Switzerland and Turkey are still excluded in the analyses due to lack of detailed land cover data and/or rural ozone data. In 2007 Switzerland and Turkey are not included. Since 2008 only Turkey is not included. Calculations of forest exposure are not available for year prior to 2004.

Rural concentration map of the ozone indicator AOT40 for forest in 2008

Note:The gradient of the AOT40f values is similar to those of the AOT40c for crops: relative low in northern Europe, and the highest values observed in the countries around the Mediterranean.
The critical level is met in north Scandinavia, Ireland, part of the UK and in the coastal regions of the Netherlands (total forested area with concentrations below the critical level is 22 % of a total area of 1.44 million km2). In south Europe levels may be as high as 4-5 times above the critical level.

Critical loads for nutrient nitrogenThe EU has a long-term objective of not exceeding critical loads for nutrient nitrogen. Excess inputs of nitrogen to sensitive ecosystems may cause eutrophication and nutrient imbalances. The critical load of nutrient nitrogen is defined as the highest atmospheric deposition of nitrogen compounds below which harmful effects in ecosystem structure and function do not occur, according to present knowledge. In 2000 rather large areas show high exceedances of critical loads for nutrient nitrogen, especially in the western part of Europe, following the coastal regions from north-western France to Denmark. In southern Europe high exceedances are only found in northern Italy.

The predictions for 2010 and 2020 indicate that the risk of exceedances is high irrespective of whether we assume that the current policies and measures to reduce eutrophying nitrogen emissions will be fully implemented (the current legislation CLE scenario) or that all technically and economically feasible additional policies are applied (the maximum feasible reduction MFR scenario).

More specifically, the area with exceedances above 1200 eq ha-1a-1 in 2010 hardly changes under the CLE scenario in 2020, while exceedances in this highest range do not occur according to the MFR scenario (see Figure 4). However, in the latter case still broad areas in Europe remain at risk of eutrophication and negative changes in nutrient balances. In these areas exceedances that range from 200 to 1 200 eq ha-1a-1 are predicted (see the border area between the Netherlands and Germany, in particular).

Critical loads for acidificationThe EU has a long-term objective of not exceeding critical loads for acidity in order to protect Europe's ecosystems from acidification. The critical load of sulphur and nitrogen acidity is defined as the highest deposition of acidifying compounds that will not cause chemical changes leading to long-term harmful effects on ecosystem structure and function.

In addition to the long-term objective, the EU has a 2010 interim environmental objective to reduce areas where critical loads are exceeded by at least 50 % in each grid cell for which critical loads exceedances are computed, compared with the 1990 situation. The exceedances of critical loads for acidification caused by the deposition of air pollutants in 1990, 2000, 2010 (current legislation scenario; CLE) and 2020 (CLE as well as maximum feasible reduction scenarios, MFR) were calculated. 84 % of the grid cells with critical loads exceedances in 1990 show a decline in exceeded area of more than 50 % by 2010. Though the interim environmental objective has strictly speaking not been met, the improvements are considerable.

Figures 5-8 show that in 2000 large areas with exceedances (i.e. higher than 1 200 eq ha-1a-1, shaded red) are mostly located in Belgium, Germany, the Netherlands and Poland. For the CLE scenario, the size of the area where critical loads are exceeded is considerably reduced in 2020. The MFR scenario shows that many areas in Europe will no longer be at risk of acidification in 2020 if all technically and economically feasible additional policies are also implemented. Nevertheless, high exceedance peaks between 700 and 1 200 eq ha-1a-1 would still be expected for ecosystems in the Netherlands.

Target values for ozone

The EU has the objective of protecting vegetation from high ozone concentrations accumulated over the growing season (defined as the summer months May to July). The target value for 2010 is 18 000 (μg/m3).hour. The long term objective is 6 000 (μg/m3).hour.

There is a substantial fraction of the agricultural area in EEA-32 member countries (excluding Turkey (see footnote [1]) where the target value is exceeded (in 2008, about 35 % of a total area of 2052 million km2). Exceedances of the target values have notably been observed in southern, central and eastern Europe (see Figure 9 and 10 - see footnote [2]). The long-term objective is met in 5 % of the total agricultural area, mainly in Ireland and Scandinavia. In 2003 the meteorological conditions were very favorable for ozone formation resulting in exceptional high concentrations. Year 2004 was a less exceptional year and substantial lower ozone levels, similar to the levels in 2001-2002, have been observed. In 2005 ozone concentrations were higher than in 2004 but the high levels of 2003 were not observed. The average ozone concentrations in 2006 are only slightly higher than in 2005. However, June and July 2006 were characterized by a large number of ozone episodes resulting in much higher AOT40 value compared to 2005. In 2007 the levels are lower again, similar to the situation in 2004. In 2008 ozone the levels showed a general increase.

There is great concern that the 2010 target will not be met. Also, it is expected that exposure of vegetation to ozone concentrations in the next decade will remain well above the long-term objective despite emission reductions of ozone precursor pollutants through EU legislation and UNECE protocols.

In addition to the EU target value, within the UNECE Convention on Long-range Transboundary Air Pollution a critical level has been defined for the protection of forest. This critical level related to the accumulated sum during the full summer (April-September) and is set to 10 000 (μg/m3).h. Figure 11 and 12 shows this AOT40 for forest (AOT40f). The gradient of the AOT40f values is similar to those of the AOT40c for crops: relative low in northern Europe, and the highest values observed in the countries around the Mediterranean. The critical level is met in north Scandinavia, Ireland, part of the UK and in the coastal regions of the Netherlands (total forested area with concentrations below the critical level is 22 % of a total area of 1.44 million km2). In south Europe levels may be as high as 4-5 times above the critical level (see Figure 11).

Figure 12 summarizes the exposure of forested areas; during the last five years large variations are observed. While in 2004 and 2006 almost all forest has been exposed to levels exceeding the critical level, in 2007 40 % was exposed to lower levels. Similar to the AOT40 for crops (see below) no clear up- or downward trend could be detected.

([1]) Until 2006 Iceland, Norway Switzerland and Turkey have not been included in the analysis due to lack of detailed land cover data and/or rural ozone data, in 2007 Switzerland and Turkey are not included and since 2008 only Turkey is not included.

Which areas in Europe remain most affected by eutrophication, acidification and ground-level ozone?

Percentage of ecosystem area at risk of eutrophication for EEA Member Countries and EEA Cooperating Countries in 2010 for a current legislation (CLE) scenario

Note:The results were computed using the 2008 Critical Loads database. Deposition data was made available by the LRTAP Convention EMEP Centre for Integrated Assessment Modelling (CIAM) at the International Institute for Applied Systems Analysis (IIASA) in autumn 2007.

Percentage of ecosystem area at risk of eutrophication for EEA Member Countries and EEA Cooperating Countries in 2020 for a CLE scenario

Note:The results were computed using the 2008 Critical Loads database. Deposition data was made available by the LRTAP Convention EMEP Centre for Integrated Assessment Modelling (CIAM) at the International Institute for Applied Systems Analysis (IIASA) in autumn 2007.

Percentage of ecosystem area at risk of eutrophication for EEA Member Countries and EEA Cooperating Countries in 2020 for a maximum feasible reduction (MFR) scenario

Note:The results were computed using the 2008 Critical Loads database. Deposition data was made available by the LRTAP Convention EMEP Centre for Integrated Assessment Modelling (CIAM) at the International Institute for Applied Systems Analysis (IIASA) in autumn 2007.

Percentage of ecosystem area at risk of acidification for EEA Member Countries and EEA Cooperating Countries in 2010 for a current legislation (CLE) scenario

Note:The results were computed using the 2008 Critical Loads database. Deposition data was made available by the LRTAP Convention EMEP Centre for Integrated Assessment Modelling (CIAM) at the International Institute for Applied Systems Analysis (IIASA) in autumn 2007.

Percentage of ecosystem area at risk of acidification for EEA Member Countries and EEA Cooperating Countries in 2020 for a CLE scenario

Note:The results were computed using the 2008 Critical Loads database. Deposition data was made available by the LRTAP Convention EMEP Centre for Integrated Assessment Modelling (CIAM) at the International Institute for Applied Systems Analysis (IIASA) in autumn 2007.

Percentage of ecosystem area at risk of acidification for EEA Member Countries and EEA Cooperating Countries in 2020 for a maximum feasible reduction (MFR) scenario

Note:The results were computed using the 2008 Critical Loads database. Deposition data was made available by the LRTAP Convention EMEP Centre for Integrated Assessment Modelling (CIAM) at the International Institute for Applied Systems Analysis (IIASA) in autumn 2007.

Percentage of natural ecosystem area at risk of acidification (left) and of eutrophication for the 32 EEA member countries and EEA cooperating countries in 2000 and for two emission scenarios: current legislation (CLE) in 2010 and 2020, maximum feasible r

Annual variation in the ozone AOT40 value for crops (May-July) in (μg/m³).h, 1996-2008

Note:Average values over all rural stations which reported data over at least nine years in the period 1996-2008. The red line corresponds to the 5-year averaged value. Variations over Europe in observed values is large, eighty percent of the observations falls with the red shaded area.

Agricultural area (in 1 000 km²) in EEA member countries for each exposure class

Note:Due to lack of detailed land cover data and/or rural ozone data Iceland and Norway are not included until 2006 and onwards. Switzerland have not been included in the analysis for the entire period 1996-2007 due to the same reasons. Turkey is not included in the analysis 1996-2008.

Estimated trend in AOT40 for crops (May-July) at rural stations operational during the period 1996-2008

Note:Estimated trend in AOT40 for crops values (May-July) at stations operational during the period 1996-2008. Only rural background stations are included. Note that at more than 90 % of the stations no significant up- or downward trend has been estimated.

Eutrophication, ecosystem area at riskThe percentage of ecosystems at risk of eutrophication and negative changes in nutrient balances has been calculated as the share of sensitive ecosystems for which deposition of oxidized and reduced nitrogen compounds exceeds the critical loads. In 13 EEA member countries the percentage of sensitive ecosystem area at risk will still be (close to) 100 % in 2010 (see Figure 11), assuming that current legislation for reducing national emissions will be fully implemented (CLE scenario). Only in five EEA member countries the area at risk is estimated to be lower than 50 %, with values below 20 % for the United Kingdom, Norway and Romania. No significant improvements are predicted for 2020 in almost all EEA countries according to the CLE scenario (see Figure 12). Nevertheless, significant improvements can be seen in 2020 in almost all countries when assuming a maximum feasible reduction scenario (MFR; see Figure 13). However, even in the case of MFR in four EEA member countries the percentage of ecosystem area at risk would still be between 90 % and 95 % (Lithuania, Latvia) or even close to 100% (Czech Republic, Denmark and Luxembourg).

Acidification, ecosystem area at riskThe percentage of sensitive ecosystems at risk of chemical changes with negative effects on ecosystem function and structure caused by acidification has been calculated as the share of sensitive ecosystems for which critical loads for acidification are exceeded by deposition of acidifying nitrogen and sulphur compounds. In general the percentage of ecosystem area at risk of acidification is much lower than the percentage of ecosystem area at risk of eutrophication. For some countries, for example Germany and Poland, the percentage of sensitive ecosystem area at risk of acidification is predicted to decrease between 2010 and 2020 according to the current legislation scenario (CLE, see Figure 14 and 15). For many other countries the suggested improvements are around five percent (e.g. for Denmark and the United Kingdom) or less (e.g. for Latvia, the Netherlands or Sweden).

With the exception of the Netherlands the sensitive ecosystem areas at risk of acidification for the maximum feasible reduction (MFR) scenario is predicted to be well below 10 % in all EEA member countries in 2020 (see Figure 16). A detailed overview of ecosystem areas at risk in EEA countries is given in Figure 17. The computed European area at risk of acidification decreases from 11 % in 2000 to 6 % and 1 % in 2020 for the CLE and MFR scenarios, respectively. The Netherlands, Poland and Denmark are the countries for which the areas at risk have been assessed to be above 30 % for the CLE scenario in 2010. With the exception of the Netherlands the sensitive ecosystem areas at risk of acidification for the MFR scenario were in 2020 well below 10 % in all EEA member countries.

The comparison of ecosystem areas exceeding the critical loads for acidification in 1990 and 2010 show that the area for the whole of Europe declined by 83 %. A high percentage (84 %) of the 50 x 50 km2 EMEP grid cells with critical loads exceedances in 1990 show a decline in exceeded area of more than 50 %. The National Emissions Ceiling Directive (2001) states that 'the area where critical loads are exceeded shall be reduced by at least 50 % (in each grid cell) compared with the 1990 situation'. Although this interim environmental objective given in the directive has not strictly speaking been achieved, the improvements are considerable.

Ecosystem exposure to ground-level ozone

Observed AOT40 for crops concentrations indicate increasing ecosystem exposure, but with large variation. Over the period 1996-2008, there are 265 rural background stations providing valid data to AirBase during at least 10 years in this 13-year period. At a majority of the stations (164) the time series have a tendency to increase although at only 16 stations this increase is statistically significant. Of the other 101 stations having a downward tendency, three stations shows a significant trend (Figure 20).

Most stations are located in north-west Europe, and with a relative small number located around the Mediterranean Sea, the selected stations are not representative for the whole of Europe. Figure 22 shows a mixed pattern in observed trends, decreasing trends seems to be observed more frequently in western, coastal regions and increasing level in continental Europe. Whilst the relatively short time series without significant trends together with meteorological fluctuations add to the difficulty in making clear conclusions on trends, the area where the target value is exceeded appears to be stable around 35-45 % of the total area during the period 1996-2008. In the EEA-32 member countries the NOx and NMVOC precursor emissions have dropped with 20-30 % in the corresponding period.

A data summary of agricultural area (in 1 000 km2) for EEA countries for each exposure class is given in the table in Figure 21. The total agricultural area in the EEA-32 member countries excluding Iceland, Norway, Switzerland and Turkey amounts to be 2 024 million km2; since 2007 Iceland and Norway are included in the analysis increasing the total agricultural area to 2 042 million km2. Since 2008 data for Switzerland is available.

Indicator specification and metadata

Indicator definition

The indicator shows the ecosystem or crops areas at risk of exposure to harmful effects of ozone as a consequence of air pollution, and shows the state of change in acidification, eutrophication and ozone levels of the European environment. The risk is estimated by reference to the 'critical level' for ozone for each location, this being a quantitative estimate of the exposure to these pollutants below which significant and harmful effects do not occur in the long term at present knowledge.

The fraction of agricultural crops that is potentially exposed to ambient air concentrations of ozone in excess of the EU target value and long-term objective set for the protection of vegetation is also shown.

Eutrophication and acidificationCritical loads of acidity and of nutrient nitrogen are employed to describe exposure to acidification and to eutrophication for forests and semi-natural areas in Europe, including Natura 2000 sites. The area where the deposition of acidifying and eutrophying pollutants is in exceedance of critical loads provides also an indication of the extent of European ecosystem area which is at risk of damage to biodiversity. By analysing the change of exceedances over time (comparative static analysis) an indication of the effects of changing air pollutant emissions over time is obtained. The magnitude of the exceedance (deposition minus critical load) is an important input to the dynamic modelling of time delays in damage. Inversely, once critical loads are no longer exceeded, recovery may take some time as well. By including the risk to be met within a legislative target and year the distance from this target can be evaluated.

OzoneAOT40 is 'Accumulated ozone exposure over a threshold of 40 ppb'. The indicator shows the ecosystem or crop areas at risk of exposure to harmful levels of ozone as a consequence of air pollution. The risk is estimated by referring to the 'critical level' of ozone for sensitive areas. Thus, the indicator is a quantitative estimate of the exposure to ozone below which significant and harmful effects do not occur in the long term according to present knowledge.The fraction of agricultural crops that is potentially exposed to ambient air concentrations of ozone in excess of the EU target value set for the protection of vegetation is also shown.

AOT40: means the sum of the differences between hourly concentrations greater than 80 µg/m3 (= 40 parts per billion) and 80 µg/m3 accumulated over all hourly values measured between 8.00 – 20.00 Central European Time. For crops the accumulation is from 1 May to 31 July. For forest the accumulation is over the summer period (1 April – 30 September). each day ozone concentrations. AOT40 is expressed in (μg/m3).hour

Regions at risk: % of total agricultural area

Change over time: % of change compared to base year.

Percentage of the arable land in Europe potentially exposed to ambient air concentrations of ozone (O3) in excess of the EU target value set for the protection of vegetation.

Rationale

Justification for indicator selection

Excess deposition of air pollutants can lead to disturbances in the function and structure [1] of ecosystems. Deposition of sulphur and nitrogen compounds contributes to the acidification of soils and freshwaters. Negative effects are the leaching of plant nutrients from soils and damage to flora and fauna (changes in biodiversity). Deposition of nitrogen compounds can lead to an oversupply of nutrient nitrogen in terrestrial and water ecosystems. Effects can be changes in vegetation abundances or leaching of nitrate to groundwater.

The risk of damage of a sensitive ecosystem receptor at a certain location can be evaluated by comparing the estimated deposition of acidifying and eutrophying air pollutants to the critical load for that location. The critical load is the deposition below which adverse effects on specified sensitive elements of an ecosystem do not occur according to present knowledge. Critical loads for several (semi-)natural areas in Europe are computed under the Convention on Long-range Transboundary Air Pollution by the Coordination Centre for Effcets (CCE; see Hettelingh et al., 2008). Thus, an ecosystem is at risk of acidification or eutrophication when its critical load is exceeded by acidifying and eutrophying air pollutants, respectively. When critical loads are exceeded the actual damage to sensitive elements of an ecosystem may involve a time delay, dependent on soil, water and vegetation properties as well as combined effects due to for example climate change.

Integrated assessment models applied for assessing the effects of air pollutant mitigation measures include information on air emissions, atmospheric dispersion and depositions of air pollutants and critical loads for a range of sensitive European ecosystems (e.g. the RAINS/GAINS model [2]. Such models have been used in support of negotiations of the sulphur protocol (Oslo, 1994) and the multi-pollutant multi-effect Protocol (Gothenburg, 1999) under the 1979 UNECE Convention on Long Range Transboundary Air Pollution (LRTAP Convention). Reductions in critical loads exceedances as short and long term objectives are also addressed in the European Union's (EU) National Emissions Ceiling Directive (NECD; 2001/81/EC) [3]. The NECD, sets slightly stricter emissions ceilings for EU Member States than those negotiated under the LRTAP Convention protocols.

Ground level ozone is one of the most prominent air pollution problems in Europe, mainly due to effects on human health, crops, and natural ecosystems. Threshold levels aiming at the protection of human health and vegetation have been set by the EU in the Air Quality Directive 2008/50/EC. Critical ozone levels for vegetation were further defined under the Convention on Long-range Transboundary Air Pollution (CLRTAP). Those environmental quality standards are exceeded in wide areas of Europe to a high extend. Ozone is a secondary pollutant formed in the atmosphere. Important precursors in Europe are nitrogen oxides and volatile organic compounds, and - to a lesser extent - carbon monoxide and methane. There is a strong chemical interaction between ozone and nitrogen oxides. Close to source, freshly emitted nitrogen monoxide may react very fast with ozone resulting in a depletion of ozone while nitrogen dioxide is formed; at larger distances to the source photochemical ozone formation might occur. High temperatures and sunlight favour ozone formation. Tropospheric ozone is further an important greenhouse gas (positive radiative forcing effect)

[1] Function = for example the ability of forest soils to buffer airborne acidifying pollutants without excessive leaching of plant nutrients to ground and surface waters; structure = e.g. loss of (protected) species[2] http://www.iiasa.ac.at/rains/gains-methodology.html?sb=10[3] The NEC Directive is currently under revision

WHO Air Quality Guidelines
The WHO air quality guidelines off er guidance to policy-makers on reducing the effects on health of air pollution: http://www.euro.who.int/__data/assets/pdf_file/0005/78638/E90038.pdf
Air quality guidelines - global update 2005: http://www.who.int/phe/health_topics/outdoorair_aqg/en/

Policy context and targets

Context description

This indicator is relevant information for the EU's 6th Environmental Action Programme (6EAP) and the Thematic Strategy on Air Pollution. The 6EAP sets the long-term objective of not exceeding critical loads. A combined ozone, acidification and eutrophication abatement strategy has been developed by the European Commission, resulting in the National Emission Ceiling Directive (2001/81/EC) and the CAFE Thematic Strategy. In this legislation, target values have been set for air pollutant emissions causing acidification and eutrophication, as well as for ozone levels and for ozone precursor emissions. The EU legislation sets for ozone both a target value (to be met in 2010) and a long-term objective. This long-term objective is largely consistent with the long-term critical level of ozone for crops as defined in the UNECE LRTAP Convention protocols to abate acidification, eutrophication and ground level ozone. Within the LRTAP Convention there is a discussion whether a concentration-base or a flux-based critical level is the best indicator for the impact on ecosystems (see, for example, EMEP,2010). As the target value and long-term objective in air quality directive are concentration-based, the AOT40 has been chosen here as relevant parameter.

Targets

National Emission Ceilings Directive 2001/81/EC, Article 5 The aim of the directive is to 'limit emissions of acidifying and eutrophying pollutants and ozone precursors in order to improve the protection in the Community of the environment and human health against risks of adverse effects from acidification, soil eutrophication and ground-level ozone and to move towards the long-term objectives of not exceeding critical levels and loads… by establishing national emission ceilings, taking the years 2010 and 2020 as benchmarks National emission ceilings with interim environmental objectives for the Community as a whole...'. The following interim environmental objectives, for the Community as a whole, by 2010 has been set for acidification: The areas where critical loads are exceeded shall be reduced by at least 50 % (in each grid cell) compared with the 1990 situation. The interim environmental objective for vegetation-related ground-level ozone exposure is: By 2010 the ground-level ozone load above the critical level for crops and semi-natural vegetation (AOT40 = 3 ppm.hour) shall be reduced by one-third in all grid cells compared with the 1990 situation. In addition, the ground-level ozone accumulated concentration shall not exceed an absolute limit of 10 ppm.hour, expressed as an exceedance of critical accumulated concentration in any grid cell.

UNECE CLRTAP Gothenburg Protocol (1999) To abate acidification, eutrophication and ground level ozone it sets emission limits with target dates. Whilst environmental quality objectives are not specified, full attainment of emission targets is intended to bring an improvement in the state of the environment estimated at:

Reduction in the European area with excessive levels of acidification from 93 million ha in 1990 to 15 million ha in 2010, and with excessive eutrophication from 165 million ha in 1990 to 108 million ha in 2010. The number of days with excessive ozone levels will be halved. The exposure of vegetation to excessive ozone levels will be 44 % less in 2010 compared to 1990.

Directive 2001/81/EC, on nation al emissions ceilings (NECD) for certain atmospheric pollutants. Emission reduction targets for the new EU10 Member States have been specified in the Treaty of Accession to the European Union 2003 [The Treaty of Accession 2003 of the Czech Republic, Estonia, Cyprus, Latvia, Lithuania, Hungary, Malta, Poland, Slovenia and Slovakia. AA2003/ACT/Annex II/en 2072] in order that they can comply with the NECD.

Methodology

Methodology for indicator calculation

Acidification and eutroficationAir emission data is reported annually by national authorities to UNECE/EMEP (Convention on Long-range Transboundary Air Pollution) and to the European Community. Reported data includes both newest estimates (two years in arrears) and recalculated emissions from previous years. Emission data is stored and verified at EMEP/CEIP (Centre on Emission Inventories and Projections) [1].Using these emissions, EMEP/MSC-W [2] calculates atmospheric transport of sulphur and nitrogen pollutants using the EMEP Unified Model at a spatial resolution of 50 x 50 km2 and according to modelled meteorological conditions adjusted towards observations.The Coordination Centre for Effects (CCE) has produced an update of the critical loads database in 2008 (Hettelingh et al., 2008) [3] for use in support of revisions of European air pollution agreements. In 2004 the CCE updated this database with national updates of critical loads (see below section on gap-filling where countries did not provide data). The CCE collaborates with IIASA (CIAM) [4] and EMEP to assess information on ecosystem specific deposition which the CCE then uses to compute and map exceedances in European natural areas including Natura 2000 areas. Nitrogen and sulphur deposition in each model grid-cell are used for calculation of the average accumulated exceedances of the critical loads, which is the area-weighted average of exceedances accumulated over all ecosystem points in an EMEP grid cell. The total area of ecosystems exposed to exceedances in a country is expressed as a percentage of the total country area. These areas are summed up to provide two estimates, one for the EU-27 Member States, and for one for a larger region comprising most countries that are Parties to the Convention on Long-range Transboundary Air Pollution (including the non-EU EEA member countries and the EEA cooperating countries).

OzoneAccording to the definition in the ozone directive, AOT40 values are calculated from hourly data measured between 08.00 and 20.00 CET at all rural background stations available in AirBase. For crops AOT40 is accumulated during the three month summer period (May-July); for forest accumulation is during the full summer (April-September). Only data series with more than 75 % valid data were considered.

The AOT40 maps have been created by combining measurements data from the rural background stations combined with the results of the EMEP dispersion model [Fagerli et al 2004] altitude field and surface solar radiation in a linear regression model, followed by the interpolation of its residuals by ordinary kriging [see de Smet et al, 2009 and reference cited therein for more details]. As altitude dataset GTOPO30 (Global Digital Elevation Model) at a resolution of 30 x 30 arcsecond has been used [ESRI, Redlands, California, USA, 2005]. The solar radiation has been obtained from ECMWF [ECMWF: Meteorological Archival and Retrieval System (MARS). It is the main repository of meteorological data at ECMWF]. Kriging is a method of spatial statistics (see e.g. N. Cressie, Statistics for spatial data, New York, 1993) which makes use of spatial autocorrelation (the statistical relationship between the monitoring points expressed in the form of variograms). Kriging weights the surrounding measured values to derive an interpolation for each location. The weights are based (i) on the distance between the measured points and the interpolated point, (ii) on the overall spatial arrangement among the measured points. The type of kriging at its parameters (in particular the parameters describing the semivariogram) are chosen in order to minimize the RMS error.

The AOT40 maps have been overlayed in a GIS with the land cover CLC2000 map. The resolution was 500 x 500 m2 to generate maps for the agricultural area at risk due to ozone exposure. Exposure of agricultural area (defined as the land cover level-1 class 2 Agricultural areas encompassing the level-2 classes 2.1 Arable land, 2.2 Permanent crops, 2.3 Pastures and 2.4 Heterogeneous agricultural areas) and forest areas (defined as the land cover level-2 class 3.1. Forests) have been calculated at the country-level.

The temporal trends have been estimated using a Mann-Kendal statistical test. This test is particularly useful since missing values are allowed and the data need not to conform to any particular distribution. Moreover, as only the relative magnitudes of the data rather than their actual measured values are used, this test is less sensitive towards incomplete data capture and/or special meteorological conditions leading to extreme values.(see Gilbert, R.O., 1987. Statistical Methods for Environmental Pollution Monitoring. Van Nostrand Reinhold, New York).

Methodology for gap filling

Acidification and eutrophicationNational submissions are used where available. For European countries which have never submitted national totals the CCE uses its European background critical load database (Hettelingh et al., 2004). Turkey has not been included in the analysis due to a not sufficient data basis for calculating critical loads.

OzoneIn the AOT40-mapping Turkey has to be excluded due to the lack of reported measurements at rural background stations. In the exposure estimates Switzerland has only been included since 2008 onwards.

Statistics for spatial data
N. Cressie (1993). Statistics for spatial data. Wiley, New York, 1993. Kriging weights the surrounding measured values to derive an interpolation for each location. The weights are based (i) on the distance between the measured points and the interpolated point, (ii) on the overall spatial arrangement among the measured points. The type of kriging at its parameters (in particular the parameters describing the semivariogram) are chosen in order to minimize the RMS error.

Uncertainties

Methodology uncertainty

OzoneThe air quality data is officially submitted according to the Exchange of Information decision (Council Decision 97/101/EC). It is assumed that the air quality data has been validated by the national data supplier. Station characteristics and representativeness is often insufficiently documented, which may imply that stations that are not representative for background conditions have been included. Methodology uncertainty is given by uncertainty in mapping AOT40 based on the interpolation of point measurements at background stations. The mean interpolation uncertainty of the map of AOT40 for crops is estimated to be about 35 %.

Data sets uncertainty

OzoneMost data have been officially submitted to the Commission under the Exchange of Information Decision (and/or to EMEP under the UN ECE Convention). Air quality monitoring station characteristics and representativeness are often not well documented and coverage of territory and in time is incomplete. The different definition of AOT40-values (accumulation during 8.00 to 20.00 CET following the Ozone Directive versus accumulation during daylight hours following the definition in the NEC Directive) is expected to introduce minor inconsistencies in the data sets. The indicator as chosen provides information on the area for which monitoring information is available. Yearly changes in monitoring density will influence the total monitored area. Due to deficiencies in meta-information, the selection of background sites may include some non-background stations, probably leading to a slight underestimation of the indicator.

The indicator is subject to year-to-year fluctuations as it is mainly sensitive to episodic conditions, and these depend on particular meteorological situations, the occurrence of which varies from year to year. For instance, the relatively favourable values for 1998 are largely due to unfavourable condition for ozone formation (in other words: '1998 was a bad summer'). 2003 was a hot 'high-ozone' summer in most of Europe. When averaging over Europe this meteorologically induced variation may be less, provided spatial data coverage is sufficient.

In spite of a generally reasonable level of accuracy and precision of ozone measurements, the indicator is rather sensitive to the precision at the reference level (40 ppb or about 80 micrograms/m3), and to the accuracy of measured ozone levels. Moreover, the number of available data series varies considerably from year to year and for some years it is very low.